As a recording medium for information signal, there have widely been used optical discs to or from which information signal is optically written or read by a light beam. If an optical disc of this type has foreign matter such as dust, fingerprint or the like adherent to the signal recording surface thereof, missing of information signal will possibly be caused during recording or playback of the optical disc and thus the information signal cannot be recorded or reproduced accurately.
To prevent adhesion to the signal recording surface of such foreign matter like dust which will possibly cause such missing of the information signal, the optical disc is usually encased in a cartridge for use as a disc cartridge.
Generally, a disc cartridge is a cartridge having an optical disc pre-encased therein. The optical disc is rotatably held in the cartridge. The cartridge has formed therein a write/read opening through which a part of the optical disc held therein is exposed to outside. A write/read head faces the optical disc thus held in the cartridge through the write/read opening to write or read information signal to or from the optical disc. The write/read opening formed in the cartridge is covered with a pair of shutter members movably installed on the cartridge at least when the disc cartridge is not used, namely, when it is not loaded in any recorder and/or player.
By covering the write/read opening in the optical disc encasing cartridge with the pair of shutter members, it is possible to prevent dust or the like from entering the cartridge and adhering to the signal recording surface of the optical disc.
Optical discs used as information signal recording media include bare ones, namely, ones not encased in any cartridge, and loadable in a recorder and/or player for write or read of information signal thereto or therefrom.
However, for loading such a bare optical disc into a recorder and/or player dedicated for a disc cartridge, a cartridge is required to encase the optical disc therein for loading into such a disc cartridge-dedicated recorder and/or player.
In the meantime, the optical discs not encased in any cartridge or similar casing and loadable in a recorder and/or player include ones having information signal recorded therein in a common format but different in diameter from each other. Such optical discs include two types: one is of 12 cm in diameter (standard size) and the other is of a smaller diameter than the first one, 8 cm for example. For use of such optical discs not encased in any cartridge and different in diameter from each other for playing by a disc cartridge-dedicated recorder and/or player, cartridges may be prepared for loading into such a recorder and/or player to encase the optical discs of different diameters, respectively. Namely, each of the optical discs may be put in a corresponding one of the cartridges before loading into the recorder and/or player.
However, the preparation of such a cartridge for each of the optical discs of different diameters will add to the number of cartridge types, difficulty of cartridge management and also to the costs of manufacturing the cartridges.